1. Field of the Invention
The present invention relates to a sheet feeding apparatus, and in particular, relates to a configuration for aligning sheets stacked on a stack tray.
2. Description of Related Arts
Traditionally, there has been known a sheet feeding apparatus that feeds a sheet to an image forming portion of an image forming apparatus such as a copying machine and a printer. In such a sheet feeding apparatus, a sheet on a stack tray is drawn by a drawing roller, and the drawn sheet is separated one by one at a separating portion that includes a sheet feeding roller and a separating member and is fed to the image forming portion of the image forming apparatus. Thus, an image is formed on a sheet at the image forming portion.
There have been known a sheet feeding apparatus including a sheet feeding cassette capable of storing about a hundred sheets, a sheet feeding apparatus including a storage chamber capable of storing a number of sheets such as several thousand sheets, and the like. Further, a sheet feeding apparatus includes a feeding roller that feeds a sheet as being contacted to an uppermost face of sheets and a separating mechanism that separates the fed sheet one by one. Here, a sheet stacked on a sheet feeding cassette or in a storage chamber is fed by the feeding roller and separated by the separating mechanism one by one, and then, the sheet is fed to the image forming portion.
In some sheet cassettes or storage chambers of sheet feeding apparatuses, a movable regulating plate is arranged to align sheets before the sheets are fed. The movable regulating plate is arranged at one end side in a sheet width direction, while a fixed regulating plate serving as a positional reference in the sheet width direction is arranged at the other end side in the sheet width direction. The movable regulating plate is elastically supported by a spring and the spring causes the movable regulating plate to urge an end part of stacked sheets in the width direction with a predetermined urging force. The sheets are moved toward the fixed regulating plate by the urging force of the movable regulating plate and aligned with the other end part of the sheets being pressed toward the fixed regulating plate. Further, the movable regulating plate, in cooperation with the fixed regulating plate, guides an end part in the width direction of the sheets fed by the feeding roller to prevent sheet skewing from occurring.
Here, when the urging force of the movable regulating plate is too large, sheets are bent and feeding malfunction is caused. When the urging force thereof is too small, sheet skewing is caused. Accordingly, the urging force of the movable regulating plate is set based on experiments and the like to have an appropriate constant value that prevent a problem from occurring with general regular paper.
Recently, it has been desired that sheets for a sheet feeding apparatus are to be diversified in kinds. With a traditional structure to apply a constant urging force to the movable regulating plate, there arise a problem of feeding malfunction due to sheet bending depending on basis weight of stacked sheets when stacked sheets are reduced in quantity, and a problem of feeding malfunction due to sheet skewing. Since thick paper having large sheet basis weight is hard and heavy, large urging force is required to be aligned. However, since thin paper having small sheet basis weight is soft, sheets are bent when the urging force is enlarged. Consequently, there arises a problem that sheets cannot be aligned.